fix(coreaudio): aggregate-device uuid collision + auto start to true

CHANGELOG.md

@@ -159,6 +159,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - **CoreAudio**: Fix default output streams silently stopping when the system default output
   device is unplugged; they now reroute automatically or report `ErrorKind::DeviceNotAvailable`.
 - **CoreAudio**: Fix undefined behaviour and silent failure in loopback device creation.
+- **CoreAudio**: Fix loopback aggregate device UID collisions between concurrent instances and after crashes.
+- **CoreAudio**: Fix loopback capture returning silence due to disabled tap auto-start.
 - **CoreAudio**: Poisoned stream locks now return `ErrorKind::StreamInvalidated` instead of 
   panicking.
 - **CoreAudio**: Fix crashes on certain drivers due to early initialization.

src/host/coreaudio/macos/loopback.rs

@@ -4,8 +4,11 @@ use std::{
     ffi::{c_void, CStr},
     mem::MaybeUninit,
     ptr::NonNull,
+    sync::atomic::{AtomicU32, Ordering},
 };
 
+static AGGREGATE_INSTANCE_COUNTER: AtomicU32 = AtomicU32::new(0);
+
 use objc2::{rc::Retained, AnyThread};
 use objc2_core_audio::{
     kAudioAggregateDeviceNameKey, kAudioAggregateDeviceTapAutoStartKey,
@@ -22,7 +25,7 @@ use objc2_core_foundation::{
     kCFTypeDictionaryValueCallBacks, CFArray, CFDictionary, CFMutableDictionary, CFRetained,
     CFString, CFStringCreateWithCString,
 };
-use objc2_foundation::{ns_string, NSArray, NSNumber, NSString};
+use objc2_foundation::{NSArray, NSNumber, NSString};
 
 use super::device::Device;
 use crate::{host::coreaudio::check_os_status, Error, ErrorKind};
@@ -86,6 +89,9 @@ impl LoopbackDevice {
     pub fn from_device(device: &Device) -> Result<Self, Error> {
         // 1 - Create tap
 
+        let pid = std::process::id();
+        let instance = AGGREGATE_INSTANCE_COUNTER.fetch_add(1, Ordering::Relaxed);
+
         // Empty list of processes as we want to record all processes
         let processes = NSArray::new();
         let device_uid = device.uid()?;
@@ -99,7 +105,9 @@ impl LoopbackDevice {
         };
         unsafe {
             tap_desc.setMuteBehavior(CATapMuteBehavior::Unmuted); // captured audio still goes to speakers
-            tap_desc.setName(ns_string!("cpal output recorder"));
+            tap_desc.setName(&NSString::from_str(&format!(
+                "cpal output recorder {pid}.{instance}"
+            )));
             tap_desc.setPrivate(true); // the Aggregate Device would be private
             tap_desc.setExclusive(true); // the process list means exclude them
         };
@@ -114,7 +122,11 @@ impl LoopbackDevice {
         let tap_uid = unsafe { tap_desc.UUID().UUIDString() };
 
         // 2 - Create aggregate device
-        let aggregate_device_properties = create_audio_aggregate_device_properties(tap_uid);
+        let aggregate_device_properties = create_audio_aggregate_device_properties(
+            tap_uid,
+            &format!("com.cpal.LoopbackRecordAggregateDevice.{pid}.{instance}"),
+            &format!("Cpal loopback aggregate {pid}.{instance}"),
+        );
         let mut aggregate_device_id: AudioObjectID = 0;
         let status = unsafe {
             AudioHardwareCreateAggregateDevice(
@@ -168,14 +180,14 @@ fn to_cfstring(cstr: &'static CStr) -> CFRetained<CFString> {
 ///     @kAudioAggregateDeviceUIDKey :
 ///         @"com.josephlyncheski.MiniMetersAggregateDevice",
 ///     @kAudioAggregateDeviceTapListKey : taps,
-///     @kAudioAggregateDeviceTapAutoStartKey : @NO,
-///     // If we set this to NO then I believe we need to make the Tap public as
-///     // well.
+///     @kAudioAggregateDeviceTapAutoStartKey : @YES,
 ///     @kAudioAggregateDeviceIsPrivateKey : @YES,
 /// };
 /// ```
 pub fn create_audio_aggregate_device_properties(
     tap_uid: Retained<NSString>,
+    agg_uid: &str,
+    agg_name: &str,
 ) -> CFRetained<CFDictionary> {
     let tap_inner = unsafe {
         let dict = CFMutableDictionary::new(
@@ -221,14 +233,12 @@ pub fn create_audio_aggregate_device_properties(
         CFMutableDictionary::set_value(
             Some(dict.as_ref()),
             &*to_cfstring(kAudioAggregateDeviceNameKey) as *const _ as *const c_void,
-            &*CFString::from_str("Cpal loopback record aggregate device") as *const _
-                as *const c_void,
+            &*CFString::from_str(agg_name) as *const _ as *const c_void,
         );
         CFMutableDictionary::set_value(
             Some(dict.as_ref()),
             &*to_cfstring(kAudioAggregateDeviceUIDKey) as *const _ as *const c_void,
-            &*CFString::from_str("com.cpal.LoopbackRecordAggregateDevice") as *const _
-                as *const c_void,
+            &*CFString::from_str(agg_uid) as *const _ as *const c_void,
         );
         CFMutableDictionary::set_value(
             Some(dict.as_ref()),
@@ -238,7 +248,7 @@ pub fn create_audio_aggregate_device_properties(
         CFMutableDictionary::set_value(
             Some(dict.as_ref()),
             &*to_cfstring(kAudioAggregateDeviceTapAutoStartKey) as *const _ as *const c_void,
-            &*NSNumber::initWithBool(NSNumber::alloc(), false) as *const _ as *const c_void,
+            &*NSNumber::initWithBool(NSNumber::alloc(), true) as *const _ as *const c_void,
         );
         CFMutableDictionary::set_value(
             Some(dict.as_ref()),